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Full text of "Text Book Of Mechanical Engineering"

Cutting Angles.                              14.1

trickles.    This cools the tool, and lessens  the friction between
tool and shaving.    For cast iron and brass these precautions are f
not needed.

There has been, up to the present, some diversity of language
regarding the angles A, B? and c (Fig. 129). Thus, in the planing tool,
A. has been termed the cutting angle, while in the lathe tool c has
been so called. Manifestly the first is the more reliable nomen-
clature; then c may be called the angle of the tool.

Their values were determined by Hart thus:—

For cast iron. .For wrought iron.   For brass.

A—Cutting angle   ......     54°     ......    55°     ......    66°

B—JR.elief angle.........      3°    ......      4°    ......      3°

C—Tool.angle   .........    51°    ......     51°    ......     63°

This supposed the least force of propulsion was required. But
if endurance of point he considered, a larger angle is usually-
given, as follows :-•-

For cast iron.  For wrought iron.   .For brass.

A.—Cutting angle  ......     70*    ......    65°    ......    80°

K—-Relief angle .........      3°    ......      4°    ......      3"

C~—Tool angle   .........    <>7&    ......    61°    ......    77°

In a lathe tool i* is termed the bottom rake, and j the top rakt,
while a third angle with top of tool, but on right, or left side, is
called side mke.

These angles will serve for any machine, and the shape of
tool and shank will be treated in its proper place.

The Screw-cutting Lathe.—Plate V. shews various
views of this, the oldest but most useful tool. The example is
the design of the Britannia Company, and has to in. centres, that
is, will accommodate work of 20 in. diameter (called in America a
20 in. lathe). 40 in. work can be turned by removing the gap
bridge A, which is bolted down and dowelled, so as to allow thtk
saddle to pass over it freely.

In all lathes the work is rotated, and the tool fixed in (usually)
a slide raV, which can he moved along the lathe bed, This ap-
pliance, the very foundation of machine-tool accuracy, was the
invention of Henry Maudslay. On account of the various
diameters to be turned, the angular velocity must be capable of